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Aggregating LandScan data to polygons

Question asked by yellie on Jul 24, 2018

Hi all,

 

I am currently working on a research project and planned to use the LandScan dataset, which provides data on ambient population. I'm very new to ArcMap and working with the LandScan data has proved to be a problematic thing for me, so I was wondering whether anyone could help. Specifically, I want to know the ambient population estimates for small geographic units in London (Lower level Super Output Areas, LSOA).   

 

The LandScan data gives me a raster file with ambient population estimates per 1km2. LSOAs are not in raster format, but I want to aggregate the values from the LandScan raster data to the LSOAs (so that I have the sum of ambient population for each LSOA in London, I need data for a total of 4829 LSOAs).

 

I have tried to do this using the ArcToolbox Function Spatial Analyst Tools —> Zonal —> Zonal Statistics as table (input feature zone data = map London with all LSOAs, zone field = LSOA, input value raster = LandScan file, statistics type = sum). Although this has provided me with a table with values per LSOA, many of my LSOA are suddenly missing (half of them have disappeared in the table - I only have 2056 LSOAs with values, and over 2000 LSOAs that exist in the zone data are not even depicted in the new table). The LandScan dataset hardly contains any missing values for London, so it’s not a missing data issue. Therefore this procedure doesn’t work in the way I want it to. 

 

I’ve been thinking about possible problems that I can't solve: 


1) The geographic coordinate system of my London map is different from the LandScan one - changing the LandScan map into British National Grid is not possible because not provided as an option). I can still load both datasets in the wrong coordinate system (so they look deformed), but that doesn’t affect my output table when I use the Zonal statistics tool (still only values for 2056 LSOAs).

2) My zone file is not a raster file and LSOA are very strangely shaped - maybe the values of rasters that don’t fall completely within a LSOA are excluded in my attribute table? I have no clue whether this is the case but it seemed like a possibility. 

 



I was hoping someone could help! 

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